Many technologies have been developed to determine, in real time, the current location of a device. For example, satellites in the global positioning system (GPS) transmit radio frequency signals from different positions in the space; and a GPS receiver receives the signals from the satellites and determines its position from the timing differences of the received signals. For example, a cellular communication device can determine or estimate its location based on cellular communication signals from basestations. For example, a wireless communication device can be configured to compute its location based on signals from a wireless communication access point.
The availability of location information of a mobile device allows the development of various location dependent services. For example, U.S. Pat. App. Pub. No. 2001/0027422 discloses a system configured to pay for location dependent services using a cellular phone as a payment device, where a service location provides a user requested service or goods based on the approximate geographical position of the cellular phone.